Complex microelectronic devices such as semiconductor chips typically require numerous connections to other electronic components. For example, a complex device including a semiconductor chip may require hundreds of electrical connections between the chip and one or more external devices. These electrical connections may be made using several alternative methods, including wire bonding, tape automated bonding and flip-chip bonding. Each of these techniques presents various problems including difficulty in testing the chip after bonding, long lead lengths, large areas occupied by the chip on a microelectronic assembly, and fatigue of the connections due to expansion and contraction of the chip and substrate during thermal cycling.
When a semiconductor chip is mounted to a circuit board, thermal expansion and contraction of the chip and circuit board can cause the contacts on the chip to move relative to contacts on the circuit board. This movement can occur during operation of the device or during manufacturing operations (e.g. when soldering the chip to the circuit board). Thus, in many microelectronic devices, in order to minimize the effects of thermal cycling, it is desirable to provide an electrical connection between components that can accommodate relative movement between the components.
One structure that has been used to successfully address thermal cycling problems is commonly referred to as a connection component such as the structures disclosed in certain preferred embodiments of commonly assigned U.S. Pat. Nos. 5,148,265, 5,148,266 and 5,455,390, the disclosures of which are hereby incorporated by reference herein. Connection components typically include a flexible sheet having a plurality of terminals thereon and flexible leads that are used to electrically interconnect the terminals with contacts on a microelectronic element, such as a semiconductor chip. The flexible leads permit thermal expansion of the microelectronic element and connection component while maintaining the electrical connection between therebetween. The terminals of the connection component may be used to test the package, and/or permanently attach the package to another microelectronic element, such as a printed circuit board. A compliant layer may be disposed between the microelectronic element and the connection component. The compliant layer typically encapsulates the leads and facilitates connection of the terminals to a test device and/or to the final electronic assembly by compensating for variations in component flatness and the heights of the terminals.
In certain preferred embodiments of commonly assigned U.S. Pat. No. 5,518,964 (“the '964 patent”), the disclosure of which is hereby incorporated by reference herein, a microelectronic package is made by first connecting flexible leads between microelectronic elements, such as a chip and a connection component, and then moving the elements away from one another through a predetermined displacement so as to bend the leads. The leads may have first ends permanently attached to the connection component and second ends releasably attached to the connection component. During assembly, the connection component may be juxtaposed with a semiconductor chip having contacts and the second ends of the leads may be bonded to the contacts on the chip. Following bonding, the connection component and chip are moved away from one another, thereby vertically extending the leads. During or after movement, a curable liquid material, such as a silicone elastomer, may be introduced between the elements. The curable material may be cured, such as by using heat, to form a compliant dielectric layer surrounding the leads. The resulting semiconductor chip package has terminals on the connection component which are electrically connected to the contacts on the chip, but which can move relative to the chip so as to compensate for thermal expansion and contraction of the elements during thermal cycling. The package may be mounted to a circuit board by solder-bonding the terminals of the connection component to conductive pads on the circuit board.
In other embodiments of the '964 patent, the package-forming process can be conducted on a wafer scale, so that all of the semiconductor chips in a wafer may be simultaneously connected to connection components. The wafer and connection components may then be moved away from one another so as to vertically extend all of the leads of the wafer in a single step. The resulting package is severed to provide individual units, each including one or more chips electrically interconnected with a portion of a dielectric body. The above-described flexible leads may be formed on the chip or wafer, rather than on the dielectric body. In further embodiments of the '964 patent, a dielectric body having terminals and leads is connected to terminal structures on a temporary sheet. The temporary sheet and dielectric body are moved away from one another so as to vertically extend the leads, and a curable liquid material is introduced around the leads and cured so as to form a compliant layer between the temporary sheet and the dielectric body. The temporary sheet is removed, leaving tip ends of the terminal structures projecting from a surface of the compliant layer. Such a component, commonly referred to as a connection component, may be used between two other components.
In certain preferred embodiments of commonly assigned U.S. Pat. No. 5,688,716, the disclosure of which is hereby incorporated by reference herein, a microelectronic package includes a chip and a package element, such as a heat sink. The chip has contacts electrically interconnected with terminals on a dielectric element, such as a sheet or plate. The dielectric element and chip are then moved away from one another to vertically extend the leads, and a curable liquid material is injected between the package element and dielectric element and around the leads. The dielectric element and the package element extend outwardly beyond the edges of the chip and physically protect the chip.
In certain preferred embodiments of commonly assigned U.S. Pat. No. 6,117,694, the disclosure of which is hereby incorporated by reference herein, a microelectronic package is made by connecting leads between a pair of microelectronic elements and then moving the elements away from one another so as to vertically extend the leads. After vertically extending the leads, a curable encapsulant may be injected between the microelectronic elements. The encapsulant may be injected under pressure for both moving the microelectronic elements away from one another and vertically extending the leads. Alternatively, the leads may be formed by retaining the microelectronic elements against respective platens by vacuum, and then moving the platens away from one another for vertically extending the leads. A curable liquid encapsulant may be injected while the platens maintain the microelectronic elements in their displaced positions.
Despite these and other advances in the art, still further improvements would be desirable. Specifically, there is a need for improved chip packages having high input/output or fine pitch contacts that may be made more easily and more economically.